Reciprocal ferrite waveguide phase shifter having means to rotate the magnetic field about an axis transverse to the longitudinal axis of the ferrite rod



3, 1966 F. REGGIA ETAL 3,268,837

RECIPRQCAL FERRITE WAVEGUIDE PHASE SHIFTER HAVING MEANS To ROTATE THE MAGNETIC FIELD ABOUT AN AXIS TRANSVERSE TO THE LONGITUDINAL AXIS OF THE FERRITE ROD Filed NOV. 6, 1963 (\6 B 2 SheetsV' Sheet 1 H6. N

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Flled Nov 6, 1963 F. REGGIA ETAL 3,268,837 RECIPROCAL FERRITE WAVEGUIDE PHASE SHIFTER HAVING MEANS TO ROTATE THE MAGNETIC FIELD ABOUT A'N AXIS TRANSVERSE TO THE LONGITUDINAL AXIS OF THE FERRITE ROD 2 Sheets-Sheet 2 PARALLEL iMAcwNET MAGNET 4ND FEREITE AXES Z MAGNETS ANGLE 0F Bnxs MAGNET (DEGREES) L00 PHASE (DEGREES) wvavrazs, fleA/vK 56604 flaw/4E0 5. Jaw/55, Je.

United States Patent 3,268,837 RECIPROCAL FERRITE WAVEGUIDE PHASE SHIFTER HAVING MEANS TO ROTATE THE MAGNETIC FIELD ABOUT AN AXIS TRANS VERSE TO THE LONGITUDINAL AXIS OF THE FERRITE ROD Frank Reggia, Bethesda, Md., and Howard S. Jones, In, Washington, D.C., assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 6, 1963, Ser. No. 321,981 6 Claims. (Cl. 33331) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalty thereon.

This invention relates to microwave devices, and more particularly to mechanically variable microwave phase shifters.

Variable phase shifters, by means of which the phase of an output wave may be shifted with respect to an input wave, are an essential component in the electromagnetic wave transmission art. Devices which have been developed in the prior art to accomplish this function fall into two classes. One class employs mechanical moving parts inside the waveguide and this class is inherently restricted to applications involving relatively low rates of variation, and small phase shifts per unit length of phase shifter. A second class of phase shifters has been developed capable of large phase shifts per unit length, and permitting the amount of phase shift introduced to be varied electrically at a rapid rate. The most common embodiment of this last type phase shifter employs the properties of gyromagnetic materials in the presence of exciting magnetic field. One example of such phase shifters is the patent issued to Arthur G. Fox, Patent No. 2,952,821. Another example is the copending application of Frank Reggia et al., Ser. No. 102,075, filed April 10, 1961, now Patent No. 3,212,031. These electrically controlled phase shifters have found wide application in such uses as electrically scannable radar antennas, and phase modulators. They commonly employ a section of waveguide having an axially mounted ferrite element with a magnetizing coil wound around the waveguide creating a magnetic field in the ferrite element when current flows through the coil. A change in the current coil results in a change in the magnitude of the magnetic field. This alters the radio frequency permeability of the ferrite element, changes the propagation constant of the microwave energy, and varies the amount of phase shift. Thus, by controlling the amplitude of the current in the coil, the phase of the propagated energy may be varied in any desired manner. With this type of phase shifter, the driving or phase-establishing current must flow continuously through the magnetizing coil. Since any variation in the amplitude of the current results in a change of the established phase shift, the current source must be extremely Well regulated, and this regulation is diflicult and expensive to obtain. For this reason, mechanical phase shifters are commonly employed in laboratory work, and other applications where rapid phase changes are not as important as long time stability. Prior art mechanical phase shifters are, however, large bulky, expensive, and employ moving parts in the propagation path of the microwave energy.

It is, therefore, an object of this invention to provide a novel mechanically variable microwave phase shifter having long time stability, and which is simple, inexpensive, compact, and employs no moving parts in the propagation path of the microwave energy.

These and other objects of this invention are accomplished by using applicants discovery that a change in direction of a magnetic field applied to a ferrite rod which is coaxially disposed in an asymmetrical waveguide section causes a variation in the phase shift of the propagated energy without causing distortion. This discovery allows applicants to construct a variable microwave phase shifter using permanent magnets. In a specific embodiment, permanent magnets are mounted adjacent to the waveguide section containing a ferrite rod, and by simply rotating the permanent magnets, the amount of phase shift introduced by the section is varied.

The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings, in which:

FIG. 1 is a partial sectional view of one embodiment of this invention.

FIG. 2 is a partial sectional view of a preferred embodiment of this invention.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2.

FIG. 4 is a plan view representational of the embodiments of either of FIGS. 1 or 2.

FIG. 5 is a plot of phase shift vs. direction of the magnetic field.

FIG. 1 shows the reciprocal mechanically variable microwave phase shifter constructed in accordance with the teachings of the present invention. The phase shifter 10 consists of a section of asymmetrical rectangular waveguide 11 with a ferrite rod 12 coaxially mounted therein. As described in the above-mentioned Reggia et al. application and as is well known to those skilled in the art, the term asymmetrical as used here refers to a waveguide structure that is not symmetrical about the xy axis having one of its dimensions below cutoff for all higher order modes and the other dimension above cutoff for only one mode, i.e. the fundamental mode. Reference numeral 16 denotes a means for producing a magnetic field in the ferrite element 12. Except for the method of varying the phase shift, the phase shifter of the present invention is constructed in accordance with principles of the aforementioned Reggia et al. application, to which reference may be made for the details of construction. Briefly, the diameter of the magnetized ferrite rod 12 is made large enough to have a substantial effect on the energy propagated in section, yet small enough to prevent Faraday rotation. The ferrite 12 is held in place by supports 14 of an insulating plastic material, such as a polyfoam, and the ferrite 12 is tapered at both ends, as designated by the numeral 15, to provide an impedance match. The elements thus far described are common to the embodiments of both FIGS. 1 and 2, and like reference numerals have been used to indicate like parts.

In the embodiment of FIG. 1 the magnetizing element 16 is a single permanent magnet mounted outside the Waveguide 11. The magnet 16 is preferably, although not necessarily, the same length as the ferrite rod 12, and is attached to the waveguide 11 by a pin 18, which permits the rotation of magnet 16. As the magnet 16 is rotated on the pin 18, the direction of the magnetizing field produced by the magnet 16 in the ferrite rod 12 is changed. Plot A of FIG. 5 shows the phase shift versus rotation for the single magnet 16, zero rotation being arbitrarily denominated as that position where the NS axis of magnet 16 is perpendicular to the longitudinal axis of the waveguide. The maximum phase shift is produced when the N-S axis of the bar magnet 16 is parallel to the longitudinal axis of the ferrite 12. With the N-S axis of the bar magnet 16 transverse to the longitudinal axis of ferrite 12 (zero rotation) no phase shift is introduced by the phase shifter 10.

Obviously, any nonlinearity between the amount of rotation of the magnet 16 and the amount of phase shift 3 introduced may be compensated for by calibration or gearing.

The embodiment of FIGS. 2 and 3 is similar in most respects to that shown and described in connection with FIG. 1. Here, rather than a single magnet as shown in FIG. 1 there are two permanent magnets 26 and 27 mounted on either side of the waveguide section 11 adjacent the ferrite rod 12. In this preferred embodiment, the bar magnets 26 and 27 are mounted on gear discs 28. The gear discs 28 engage gears 32 and 33 which are mounted on a shaft 35 and held in place by bracket 34. The shaft 35 has a telescoping socket and plug joint 36 which may be locked by a pin 37. With pin 37 in place magnets 26 and 27 may be rotated in unison by turning knob 31. If fine adjustment is desired, the pin 37 may be removed and the magnets rotated independently.

In order to concentrate a strong magnetic field in the ferrite rod 12 with relatively small permanent magnets 26 and 27, the magnets 26 and 27 are mounted with similar poles aligned, as shown in FIGS. 2 and 3. The opposing fields produced by the magnets concentrate in the centrally placed ferrite rod 12. As was the case in the embodiment of FIG. 1, rotation of the direction of the field produced by the magnets 26 and 27 produces a variation in the amount of phase shift introduced by the phase shifter as shown in plot B of FIG. 5. Again, when the direction of the magnetic field is perpendicular to the longitudinal axis of the ferrite rod 12, the phase shifter has no measurable effect on the propagation of microwave energy. As the direction of the magnetic field is then rotated in either direction, there is an increasingly large phase shift or delay of the microwave energy, until a maximum phase shift occurs when the N-S axis of the permanent magnets 26 and 27 coincide with the longitudinal axis of the ferrite rod 12.

The plot B of FIG. gives actual values obtained with a phase shifter constructed in accordance with the teachings of this invention, as embodied in FIGS. 2 and 3. The operating frequency was 9700 mc., and the inside dimensions of the waveguide were 0.900 x 0.400 inch. The length of the ferrite rod was 2% inches with inch tapers, and a diameter of 0.270 inch. The two magnets were A x A; x 1% inch Alnico magnets. The plot C of FIG. 5 shows the voltage standing wave ratio of this embodiment.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim as our invention:

1. A mechanical waveguide phase shifter comprising:

(a) a rectangular asymmetrical waveguide section with a ferrite rod coaxially disposed therein,

(b) means outside said waveguide section to produce a magnetic field in said ferrite element, and

(c) means to change the direction of said magnetic field about an axis transverse to the longitudinal axis of said ferrite rod.

2. A mechanical microwave phase shifter comprising:

(a) a rectangular waveguide reciprocal phase shifter including a section of asymmetrical rectangular waveguide with a ferrite rod coaxially disposed therein,

(b) means to produce a magnetic field in said ferrite rod including a permanent magnet mounted on the outside of said waveguide section adjacent said ferrite rod, said magnet being rotatable about an axis transverse to the longitudinal axis of said ferrite rod so as to change the direction of the magnetic field in said ferrite rod.

3. A mechanical waveguide phase shifter comprising:

(a) a rectangular waveguide reciprocal phase shifter including an asymmetrical waveguide section with a ferrite rod coaxially disposed therein,

(b) a permanent magnet rotatably mounted outside said waveguide section adjacent said ferrite rod.

(c) means to rotate said magnet about an axis transverse to the longitudinal axis of said ferrite rod, whereby the magnetic field produced by said magnet may be made to vary in direction with respect to the longitudinal axis of said ferrite rod causing a varying phase shift in microwave energy propagated in said phase shifter.

4. A mechanical Waveguide phase shifter comprising:

(a) a rectangular waveguide reciprocal phase shifter including an asymmetrical rectangular waveguide section with a ferrite rod coaxially disposed therein,

(b) a pair of permanent magnets located outside said waveguide section, adjacent to and on opposite sides of said ferrite rod,

(c) like poles of said pair of magnets being in alignment whereby the magnetic field of said magnets is concentrated midway between them,

(d) means to rotate said magnets about a centrally located axis perpendicular to the longitudinal axis of said ferrite rod, whereby the direction of said magnetic field produced by said permanent magnets may be varied to vary the amount of phase shift.

5. A mechanical microwave phase shifter as in claim 4 wherein said means to rotate said pair of magnets rotates them in unison.

6. A mechanical microwave phase shifter as in claim 4 wherein said means to rotate includes a clutch which, when engaged, causes said magnets to be rotated in unison, and when disengaged allows said magnets to be rotated separately.

References Cited by the Examiner UNITED STATES PATENTS 4/ 1957 Fox. 

1. A MECHANICAL WAVEGUIDE PHASE SHIFTER COMPRISING: (A) A RECTANGULAR ASYMMETRICAL WAVEGUIDE SECTION WITH A FERRITE ROD COAXIALLY DISPOSED THEREIN, (B) MEANS OUTSIDE SAID WAVEGUIDE SECTION TO PRODUCE A MAGNETIC FIELD IN SAID FERRITE ELEMENT, AND (C) MEANS TO CHANGE THE DIRECTION OF SAID MAGNETIC FIELD ABOUT AN AXIS TRANSVERSE TO THE LONGITUDINAL AXIS OF SAID FERRITE ROD. 